1. Field of the Invention
The present invention relates to a method for producing a liquid discharge head for discharging a liquid droplet such as an ink droplet, thereby forming a record on a recording medium, and more particularly to a method for producing a liquid discharge head for ink jet recording.
2. Description of the Related Art
The ink jet recording method is one of the so-called non-impact recording methods. Such an ink jet recording method generates almost negligible noise during recording and is capable of high speed recording. Also the ink jet recording method is capable of recording on various recording media and achieving ink fixation even on so-called plain paper to provide a high definition image inexpensively. Based on these advantages, the ink jet recording method has become widespread recently not only in a printer constituting peripheral computer equipment, but also as recording means for a copying machine, a facsimile apparatus, a word processor, etc.
For achieving ink discharge in the commonly utilized ink jet recording method, methods of employing, as an element for generating a discharge energy to be used for discharging an ink droplet, an electrothermal converting element such as a heater or an electromechanical converting element such as a piezo element are known. The discharge of the ink droplet can be controlled by an electrical signal in either method. The ink discharging method employing the electrothermal converting element is based on a principle of applying a voltage to the electrothermal converting element, thereby causing the ink in the vicinity of the electrothermal converting element to boil instantaneously and discharging an ink droplet at a high speed by a rapid growth of a bubble generated by a phase change in the ink at boiling. On the other hand, the ink discharge method utilizing the piezoelectric element is based on a principle of applying a voltage to the piezoelectric element, thereby causing a displacement therein and discharging an ink droplet by a pressure generated by such displacement.
The ink discharge method utilizing the electrothermal converting element has advantages of not requiring a large space for providing the discharge energy generating element and of a simple structure of the liquid discharge head, enabling easy integration of nozzles. On the other hand, such an ink discharge method is associated with drawbacks specific to this method, such as a fluctuation in the volume of the flying ink droplet by an accumulation in the liquid discharge head of the heat generated by the electrothermal converting element, a detrimental influence of a cavitation phenomenon caused by the extinction of the bubble on the electrothermal converting element, and a detrimental influence of air dissolved in the ink, forming bubbles remaining in the liquid discharge head and influencing the discharge characteristics of the ink droplet and the quality of the obtained image.
For solving these problems, Japanese Patent Application Laid-open Nos. 54-161935, 61-185455, 61-249768, and 4-10941 disclose an ink jet recording method and a liquid discharge head. The ink jet recording method disclosed in these references has a configuration in which a bubble, generated by driving an electrothermal converting element with a recording signal, is made to communicate with the external air. Such an ink jet recording method enables the stabilization of the volume of the flying ink droplet, the discharge of an ink droplet of an extremely small volume at a high speed, and the elimination of the cavitation at the extinction of the bubble thereby improving the durability of the heater, thus allowing easier obtainment of an image of a higher definition. The aforementioned references disclose a configuration, for causing the bubble to communicate with the external air, in which a minimum distance between an electrothermal converting element and a discharge port is significantly reduced in comparison with a prior configuration.
Now there will be explained such a prior liquid discharge head. A prior liquid discharge head is provided with an element substrate on which an electrothermal converting element for ink discharge is provided and an orifice substrate for constituting an ink flow path by being adjoined to the element substrate. The orifice substrate has plural discharge ports for discharging ink, plural nozzles in which the ink flows, and a supply chamber for supplying such nozzles with the ink. A nozzle is constituted of a bubble generating chamber for generating a bubble in the ink therein by an electrothermal converting element and a supply path for supplying the bubble generating chamber with the ink. The element substrate is provided with an electrothermal converting element so as to be positioned in the bubble generating chamber. The element substrate is also provided with a supply aperture for supplying the supply chamber with the ink from a rear surface opposite to a principal plane adjacent to the orifice substrate. Also, the orifice substrate is provided with a discharge port in a position opposed to the electrothermal converting element provided on the element substrate.
In the prior liquid discharge head of the above-described configuration, the ink supplied from the supply aperture to the supply chamber is supplied along each nozzle and is filled in the bubble generating chamber. The ink filled in the bubble generating chamber is caused to fly, by a bubble generated by a film boiling caused by the electrothermal converting element, in a direction substantially perpendicular to the principal plane of the element substrate and is discharged from the discharge port.
In a recording apparatus equipped with the aforementioned liquid discharge head, a higher recording speed is being investigated for achieving a higher quality, a higher definition and a higher resolution in the recorded image. For increasing the recording speed in the prior recording apparatus, U.S. Pat. Nos. 4,882,595 and 6,158,843 disclose a method of increasing a number of discharges of the flying ink droplets in each nozzle of the liquid discharge head, namely increase a discharge frequency.
In particular, U.S. Pat. No. 6,158,843 proposes a configuration of improving the ink flow from the supply aperture to the supply path, by providing a space for locally constricting the ink flow path and a projection-shaped fluid resistance element in the vicinity of the supply aperture.
However, in the aforementioned prior liquid discharge head, at the discharge of an ink droplet, the bubble grown in the bubble generating chamber pushes back a part of the ink in the bubble generating chamber into the supply path. For this reason, the prior liquid discharge head is associated with a drawback that a discharge amount of the ink droplet decreases as a result of a decrease in the ink volume in the bubble generating chamber.
Also in the prior liquid discharge head, when a part of the ink in the bubble generating chamber is pushed back toward the supply path, a part of the pressure of the growing bubble at the side of the supply path escapes into the supply path, or a pressure loss is generated by a friction between an internal wall of the bubble generating chamber and the bubble. For this reason, the prior liquid discharge head is associated with a drawback of a reduced discharge speed of the ink droplet as a result of a reduction of the bubble pressure.
Furthermore, in the prior liquid discharge head, because the volume of the ink of a very small amount filled in the bubble generating chamber varies by the bubble growing in the bubble generating chamber, there results a drawback of a fluctuation in the discharge amount of the ink droplet.